Reconciling a national methane emission inventory with in-situ measurements

Thermal processes and secondary recycling regulate the atmospheric levels of the highly toxic polychlorinated naphthalenes in the urban environment of Eastern Mediterranean and Middle East

Although production of legacy industrial-grade persistent organic pollutants has been prohibited since the early 2000's, residues persist across all environmental compartments, with unintentional releases still documented globally. The present work explores comprehensively the atmospheric occurrence and fate of the scarcely monitored polychlorinated naphthalenes (PCNs), along with polybrominated diphenyl ethers (PBDEs), in the urban environment of Eastern Mediterranean and Middle East. Gaseous and particulate phase concentrations of PCNs and PBDEs (fifty-six and twelve congeners) were comparable to urban locations in the broader region. For PCNs, regressions of partial pressure against ambient temperature revealed secondary recycling from local contaminated surfaces. Enthalpies of surface-air exchange (∆HSA) were significantly correlated to vaporization enthalpies (∆HV), corroborating short-range revolatilization processes. Molecular concentration ratios suggested inputs from thermal processes, whereas potential evaporation from Aroclor-contaminated surfaces cannot be excluded. An inverse pattern for PBDEs was observed. The regression slopes were shallow, implying advective inflows of urban air, whereas ∆HSA were insignificantly correlated with ∆HV, suggesting that, unlike PCNs, volatilization sources for PBDEs were of minor importance. Gas/particle partitioning was also evaluated by utilizing a wide range of traditional and novel models. Additionally, temperature-dependent quantitative structure-property relationship (QSPR) models were constructed separately for PCNs and PBDEs. Mixed sorptive and absorptive models yielded adequate predictions for PCNs, while steady-state models performed better for PBDEs. Both QSPR models demonstrated robust predictive capabilities across the congener groups and could serve as reference for studies under similar temperature ranges worldwide.

Hyperspectral remote sensing for air pollutants: Stereoscopic monitoring, source localization & warning, and a dynamic emission inventory concept

With the continuous improvement of air quality in China, the characteristics of emission sources of pollutants have changed significantly, from their distribution to emitted atmospheric species and the corresponding emission concentrations and source localization has become increasingly challenging. The localization uncertainties of in situ observations are further amplified when combined with model simulations, which seriously restricts the realization of China's strategic goal of "reducing pollution and carbon." In this study, we established a localization and emission warning scheme for emission sources based on various hyperspectral remote sensing techniques with different observation spatial resolutions. These include satellite remote sensing, horizontal remote sensing, Unmanned Aerial Vehicle (UAV) remote sensing, and imaging. Based on this study, we aimed to locate high-concentration emission sources of NO2 (coal-fired power plants), HCHO (chemical and coking industries), and CH2CCH3CHO (metallurgical and material synthesis industries) and provide excess emission warnings for these species. Moreover, hyperspectral imaging remote sensing technology provides a possible method to obtain a dynamic emission inventory of pollutants, and the emission concentrations of NO2, SO2, HCHO, CHOCHO, and CH2CCH3CHO emitted from the coking industry at different timescales were obtained. The localization and emission warning scheme of pollutants established based on stereoscopic remote sensing, as well as the dynamic emission inventory established based on hyperspectral imaging remote sensing, provides technical and data support for air pollution control efforts.

Innovative drone-based methodology for quantifying methane emissions from landfills

An accurate measurement of anthropogenic methane emissions is essential for improving the representation of greenhouse gas inventories and for mitigating the effects of climate change. Often, theoretical models overestimate actual emission values, while field measurements tend to be costly and/or labour-intensive. Landfills represent an important emission sector, necessitating continued investment in innovation and technology to limit fugitive emissions, particularly of methane. This study presents a novel method based on a mass balance approach to estimate fugitive methane emissions from landfills and has been tested at a solid waste landfill in Italy. Measurements were acquired using a drone equipped with a sensor, completed in just a few minutes and processed directly in the field. Results from two tests conducted a month apart are provided, each consisting of two downwind flights at the site. Emission rates varied from 320 ± 280 mg m-2h-1 to 578 ± 385 mg m-2h-1. The data was subsequently compared with the results obtained using the flux chamber method during the second test, highlighting values that were 2 to 4 times higher than those from the ground-based method. The findings of this study highlight the potential of UAV-based methodologies for measuring methane emissions compared to traditional methods. The speed of execution and processing is indeed crucial to providing accurate data and optimising both timings and flight models during an investigation.

The Role of Emission Size Distribution on the Efficacy of New Technologies to Reduce Methane Emissions from the Oil and Gas Sector

Methane emissions from oil and gas operations exhibit skewed distributions. New technologies such as aerial-based leak detection surveys promise cost-effective detection of large emitters (greater than 10 kg/h). Recent policies such as the US Environmental Protection Agency (EPA) methane rule that allow the use of new technologies as part of leak detection and repair (LDAR) programs require a demonstration of equivalence with existing optical gas imaging (OGI) based LDAR programs. In this work, we illustrate the impact of emission size distribution on the equivalency condition between the OGI and site-wide survey technologies. Emission size distributions compiled from aerial measurements include significantly more emitters between 1 and 10 kg/h and lower average emission rates for large emitters compared to the emission distribution in the EPA rule. As a result, we find that equivalence may be achieved at lower site-wide survey frequencies when using technologies with detection thresholds below 10 kg/h, compared to the EPA rule. However, equivalence cannot be achieved with a detection threshold of 30 kg/h at any survey frequency, because most emitters across most US basins exhibit emission rates below 30 kg/h. We find that equivalence is a complex tradeoff among technology choice, design of LDAR programs, and survey frequency that can have more than one unique solution set.